Hydrolytic Stability of Phosphorus Sulphides

The phosphorus sulphides differ in their hydrolytic stabilities which fall in the order  

The sesquisulphide, P4S3, is very stable in cold or hot water and is slowly attacked in acid solution. On the other hand, P4S7 is readily attacked by atmospheric moisture, evolving HjS. 

Phosphorus sulphide hydrolyses are complex processes involving the initial rupture of P-S-P followed by the P-P linkages (where present), and the eventual replacement of S by O. There have been conflicting reports about the nature of the products, which depend on pH, temperature and other factors. 

The decasulphide, P4S10, is stable in cold moist air, but acid hydrolysis at 100°C quickly produces only orthophosphate (4.94). Alternatively, if cautious alkaline hydrolysis is carried out, various thio-ated ortho anions (Chapter 9.10) can be formed as intermediate products (Table 4.17). These later react under oxidative conditions to give mostly orthophosphate, PO4 , together with some phosphorous HPOf and hypophosphorous HjPOj anions. In addition, traces of phosphine, PH3, may be produced. 

Phosphorus monosulphide, (PS) , hydrolyses in moist air strictly according to (4.95). 

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